In order to prevent poisoning, explosion and the like accidents due to leakage of gas or the like from occuring, safety shut-off valve which detect such leakage of gas or the like and automatically shut off the supply of such gas or the like have heretofore been developed. However, such conventional safety shut-off valves have such disadvantages that two electromagnetic valves are required, constructions of the valves become expensive, and controls of such constructions come to be complicated. Besides there is such a disadvantage that a conventional apparatus cannot particularly give an alarm, even if the apparatus was in shut-off condition by the leakage of gas or the like. Furthermore, conventional apparatuses are not provided with such means by which an apparatus cannot be reset until it is confirmed that there is no more leakage of gas or the like on the secondary side after the shut-off action was once effected. Thus, conventional safety shut-off valves are not sufficient in view of safety.